However, no casualties have been reported from the blast site.
"There was a low intensity blast, two live bombs were also found which were defused later, no casualties or injuries," said Senior Superintendent of Police, Jitendra Rana, Senior Superintendent of Police.
The explosion caused panic among the residents of the area. The police later recovered two high-intensity live bombs from the building. On investigation, police found them to be equipped with the same timer device – of Lotus brand – that was used in the bombs that went off in 2013 at Narendra Modi's rally at Gandhi Maidan ahead of the Lok Sabha polls and at Bodh Gaya.
No arrests have been made yet but the police have sealed the building and a two-wheeler parked at the building has also been seized.
According to local residents, the two people, who lived in the flat, are natives of Nalanda district. They are absconding even as several police teams are at work to trace them.
Reports claimed that the building was being used as a bomb making factory.
Meanwhile, a National Investigation Agency (NIA) team is en route to Patna today to assist in the probe.